Electronic device, control method for electronic device, and control program for electronic device

ABSTRACT

An electronic device includes: a monitor unit configured to monitor a speed and a position of a host car and a preceding car; a reception unit configured to receive traffic signal information including at least a current display state of a traffic light in an intersection and timing information of a change of the display state of the traffic light; a prediction unit configured to generate a first prediction result and a second prediction result; and a warning unit configured to give a first-stage warning when the first prediction result indicates that the preceding car will go into the intersection after the traffic light changes to the red signal display state, and give a second-stage warning when the second prediction result indicates that the preceding car cannot stop without braking suddenly.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromPCT application No. PCT/JP2014/005173, filed Oct. 10, 2014, which claimspriority from Japanese patent application No. 2014-016389, filed on Jan.31, 2014 and Japanese patent application No. 2014-067393, filed on Mar.28, 2014, the disclosure of which is incorporated herein in theirentirety by reference.

BACKGROUND

The present invention relates to an electronic device, a control methodfor an electronic device, and a control program for an electronicdevice, and in particular to an electronic device, a control method foran electronic device, and a control program for an electronic device fornotifying an occupant of necessary information based on received trafficsignal information.

Among electronic devices mounted in cars, an electronic device forpreventing a following car from bumping into a host car has beenpreviously known. For example, Japanese Unexamined Patent ApplicationPublication No. 2012-088964 discloses an electronic device that:receives information on a traffic light present in the travelingdirection of the host car, the road on which the host car is traveling,and the like that is transmitted from a facility installed on the road,such as an optical beacon; and when the received information indicates ared signal display, predicts that a probability that the driver of thehost car will perform an operation for reducing the speed is high, anddraws the attention of the following car at a timing earlier than thetiming when the probability of the operation for reducing the speed ofthe host car is low. In this way, it is possible to prevent thefollowing car from bumping into the host car.

SUMMARY

However, although the related-art electronic device disclosed inJapanese Unexamined Patent Application Publication No. 2012-088964 canprevent the following car from bumping into the host car, it does notgive any consideration to a risk that when a vehicle preceding the hostcar suddenly stops because a traffic light installed in the travelingdirection of that vehicle changes to a red signal display, the host carcould bump into the preceding vehicle.

To solve the above-mentioned problem, an electronic device according tothe exemplary embodiment includes: a monitor unit configured to monitora traveling speed and a traveling position of a host car, and a speedand a position of a preceding car, the host car being a vehicle in whichthe electronic device is mounted, the preceding car being a vehicletraveling ahead of the host car; a reception unit configured to receivetraffic signal information including at least a current display state ofa traffic light in an intersection located ahead of the host car in atraveling direction and timing information of a change of the displaystate of the traffic light; a prediction unit configured to generate afirst prediction result of a prediction whether or not the preceding carwill go into the intersection after the traffic light changes to a redsignal display state when the preceding car maintains a current speedbased on monitor information and the traffic signal information receivedby the reception unit, and generate, at a timing when the traffic lightbecomes the yellow signal display state, a second prediction result of aprediction whether or not the preceding car can stop before theintersection without braking suddenly based on the position and thespeed of the preceding car and a distance between the preceding car andthe intersection, the monitor information including the traveling speedand the traveling position of the host car and the speed and theposition of the preceding car monitored by the monitor unit; and awarning unit configured to give a first-stage warning when the firstprediction result indicates that the preceding car will go into theintersection after the traffic light changes to the red signal displaystate, and give a second-stage warning when the second prediction resultindicates that the preceding car cannot stop before the intersection.

Further, to achieve the above-described object, a control method for anelectronic device according to the exemplary embodiment includes: amonitoring step for monitoring a traveling speed and a travelingposition of a host car, and a speed and a position of a preceding car,the preceding car being a vehicle traveling ahead of the host car; areceiving step for receiving traffic signal information including atleast a current display state of a traffic light in an intersectionlocated ahead of the host car in a traveling direction and timinginformation of a change of the display state of the traffic light; apredicting step for generating a first prediction result of a predictionwhether or not the preceding car will go into the intersection after thetraffic light changes to a red signal display state when the precedingcar maintains a current speed based on monitor information and thetraffic signal information received in the receiving step, andgenerating, at a timing when the traffic light becomes the yellow signaldisplay state, a second prediction result of a prediction whether or notthe preceding car can stop before the intersection without brakingsuddenly based on the position and the speed of the preceding car and adistance between the preceding car and the intersection, the monitorinformation including the traveling speed and the traveling position ofthe host car and the speed and the position of the preceding carmonitored in the monitoring step; and a warning step for giving afirst-stage warning when the first prediction result indicates that thepreceding car will go into the intersection where after the trafficlight changes to the red signal display state, and giving a second-stagewarning when the second prediction result indicates that the precedingcar cannot stop before the intersection without braking suddenly.

Further, to achieve the above-described object, a control program for anelectronic device according to the exemplary embodiment for causing acomputer to execute: a monitoring step for monitoring a traveling speedand a traveling position of a host car, and a speed and a position of apreceding car, the preceding car being a vehicle traveling ahead of thehost car; a receiving step for receiving traffic signal informationincluding at least a current display state of a traffic light in anintersection located ahead of the host car in a traveling direction andtiming information of a change of the display state of the trafficlight; a predicting step for generating a first prediction result of aprediction whether or not the preceding car will go into theintersection after the traffic light changes to a red signal displaystate when the preceding car maintains a current speed based on monitorinformation and the traffic signal information received in the receivingstep, and generating, at a timing when the traffic light becomes theyellow signal display state, a second prediction result of a predictionwhether or not the preceding car can stop before the intersectionwithout braking suddenly based on the position and the speed of thepreceding car and a distance between the preceding car and theintersection, the monitor information including the traveling speed andthe traveling position of the host car and the speed and the position ofthe preceding car monitored in the monitoring step; and a warning stepfor giving a first-stage warning when the first prediction resultindicates that the preceding car will go into the intersection after thetraffic light changes to the red signal display state, and giving asecond-stage warning when the second prediction result indicates thatthe preceding car cannot stop before the intersection without brakingsuddenly.

Further, to achieve the above-described object, a control program for anelectronic device according to the exemplary embodiment for causing acomputer to execute: a monitoring step for monitoring a traveling speedand a traveling position of a host car, and a speed and a position of apreceding car, the preceding car being a vehicle traveling ahead of thehost car; a receiving step for receiving traffic signal informationincluding at least a current display state of a traffic light locatedahead of the host car in a traveling direction thereof and informationon a timing when the display of the traffic light is changed; apredicting step for generating a first prediction result of a predictionwhether or not the preceding car will go into the intersection where thetraffic light changes to a red signal display state when the precedingcar maintains a current speed thereof based on monitor information andthe traffic signal information received in the receiving step, andgenerating a second prediction result of a prediction whether or not thepreceding car can stop before the intersection where the traffic lightbecomes the red signal display state without braking suddenly based onthe position and the speed of the preceding car and a distance betweenthe preceding car and the intersection, the monitor informationincluding the traveling speed and the traveling position of the host carand the speed and the position of the preceding car monitored in themonitoring step; and a warning step for giving a first-stage warningwhen the first prediction result indicates that the preceding car willgo into the intersection where the traffic light changes to the redsignal display state, and giving a second-stage warning when the secondprediction result indicates that the preceding car cannot stop beforethe intersection where the traffic light is in the red signal displaystate without braking suddenly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary embodiment of an electronicdevice;

FIG. 2 is a flowchart for explaining an operation in a first exemplaryembodiment of an electronic device;

FIG. 3 is a graph showing a relation shown in Table 3, i.e., a relationbetween speeds of a preceding car and distances to an intersectionobtained when a traffic light becomes a yellow signal display state andthree types of threshold settings;

FIG. 4 is a flowchart for explaining an operation in a second exemplaryembodiment of an electronic device;

FIG. 5 is a flowchart for explaining an operation in a third exemplaryembodiment of an electronic device;

FIG. 6A is a flowchart for explaining an operation in a fourth exemplaryembodiment of an electronic device;

FIG. 6B is a figure for explaining operations in main steps of thefourth exemplary embodiment of the electronic device;

FIG. 7A is a flowchart for explaining an operation in a fifth exemplaryembodiment of an electronic device;

FIG. 7B is a figure for explaining operations in main steps of the fifthexemplary embodiment of the electronic device;

FIG. 8A is a flowchart for explaining an operation in a sixth exemplaryembodiment of an electronic device; and

FIG. 8B is a figure for explaining operations in main steps of the sixthexemplary embodiment of the electronic device.

DETAILED DESCRIPTION

Next, exemplary embodiments are explained with reference to thedrawings.

FIG. 1 is a block diagram of an exemplary embodiment of an electronicdevice. In the figure, a navigation device 100, which is an electronicdevice according to this exemplary embodiment, is mounted in a vehicle(hereinafter called a “host car”) of a user (a driver) and has afunction of displaying map information for the user, a function ofguiding the user through a route, and so on. Further, the navigationdevice 100 can externally receive information such as trafficinformation, display a still image or a moving image of a periphery ofthe vehicle taken by an image pickup device 201, and so on.

The navigation device 100 includes a signal reception unit 101, adetection unit 102, a vehicle-speed sensor 103, a GPS unit 104, acontrol unit 105, a storage unit 106, a communication unit 107, anoperation unit 108, and a display unit 109. The detection unit 102, thevehicle-speed sensor 103, the GPS unit 104, and the control unit 105,together with an image pickup device 201 and a sensor 202, constitutemonitor means. Further, the control unit 105 constitutes predictionmeans and also constitutes, together with at least one of the displayunit 109 and a sound output device 203, warning means.

The signal reception unit 101 constitutes reception means and receivestraffic signal information transmitted by a road-side unit installed ina road-side position located, for example, 300 m before an intersectionwith a traffic light in the vehicle approaching direction. The trafficsignal information is transmitted, for example, by an optical beacon(DSSS Level 2). The traffic signal information is information includinga current display state (red/yellow/blue) of the traffic light and thenumber of seconds before the display of the traffic light changes fromblue to red or from red to blue next time. The signal reception unit 101supplies the received traffic signal information to the control unit105.

The detection unit 102 receives information on an image of what ispresent ahead of the host car with the navigation device 100 mountedtherein in the traveling direction thereof which is taken andtransmitted by the image pickup device 201. Further, the detection unit102 receives information on a distance between the host car and avehicle traveling ahead of the host car in the traveling directionthereof (hereinafter called a “preceding car”) and a relative speedbetween the host car and the preceding car from the sensor 202. Further,the detection unit 102 detects information on an image of the precedingcar from the image taken by the image pickup device 201 by using animage recognition technique and supplies the detection informationreceived from the sensor 202 to the control unit 105.

The vehicle-speed sensor 103 measures a pulse signal that changesaccording to, for example, the rotation of the output shaft or thedriven wheel of a transmission and thereby detects the speed of the hostcar. The vehicle-speed sensor 103 supplies the vehicle-speed informationto the control unit 105. The GPS unit 104 has a publicly-knownconfiguration for receiving signals transmitted from a plurality of GPSsatellites that constitute a publicly-known GPS (Global PositioningSystem) and thereby measuring the position (a latitude, a longitude, andthe like) of the host car. The GPS unit 104 supplies positioninformation indicating the measured position of the host car to thecontrol unit 105.

The control unit 105 includes, for example, a CPU (Central ProcessingUnit), a ROM (Read Only Memory), a RAM (Random Access Memory), aninternal timer, and so on. The control unit 105 controls the wholenavigation device 100 in a centralized manner, for example, by havingthe CPU execute a program stored in the ROM. The control unit 105predicts whether or not the preceding car will stop at an intersectionthrough a later-described process based on the traffic signalinformation supplied from the signal reception unit 101, the detectioninformation supplied from the detection unit 102, the vehicle-speedinformation supplied from the vehicle-speed sensor 103, the positioninformation supplied from the GPS unit 104, and so on. As a result ofthe prediction, if necessary, the control unit 105 supplies warninginformation to the sound output device 203 and/or the display unit 109.Alternatively, the control unit 105 supplies warning information to anexternal device 204 through the communication unit 107.

The storage unit 106 stores information necessary for a display and aroute search, such as map information (road information) and variousimages. The storage unit 106 reads necessary information and supplies itto the control unit 105 in response to a request from the control unit105. The storage unit 106 includes at least one of variouspublicly-known storage media such as an HDD (Hard Disk Drive), anoptical disk, a memory card, and a semiconductor storage device. Thecommunication unit 107 transmits/receives information necessary forcommunication to/from the external device 204 through a connector(cable) in conformity with a certain standard. Note that when thenavigation device 100 is connected to the external device 204 inconformity with a wireless standard, the communication unit 107transmits/receives information necessary for communication to/from theexternal device 204 in conformity with that wireless standard.

The operation unit 108 includes a touch panel or the like disposed onthe front surface of the display unit 109 and receives an operation (aninstruction input or the like) from a user. Note that the operation unit108 may be an infrared remote controller or the like, or may be ahardware key disposed on the housing of the operation unit 108. Thedisplay unit 109 includes, for example, a liquid crystal display deviceor the like and displays a map image (a road image) and the like. Notethat the display unit 109 may not be disposed in the navigation device100. That is, the navigation device 100 may be connected to a separateexternal display device. When this external display device is a displaydevice with a touch panel, the operation unit 108 may also be anexternal device.

The navigation device 100 is connected to the external image pickupdevice 201 and the external sound output device 203. The image pickupdevice 201 includes, for example, a camera or the like. Further, theimage pickup device 201 takes an image of what is present ahead of thehost car in the approaching direction thereof and supplies theimage-taking information to the detection unit 102. The sensor 202 is,for example, a radar sensor or the like, and detects the distancebetween the host car and the preceding car traveling ahead of the hostcar and the relative speed between the host car and the preceding car.The sound output device 203 includes, for example, a speaker or the likeand outputs a guidance sound of the navigation device 100 and a warningsound.

Next, processes for deciding to make a sudden stop and for warningperformed by the navigation device 100 having the above-describedconfiguration according to this exemplary embodiment are explained withreference to FIG. 2. FIG. 2 is a flowchart for explaining an operationin a first exemplary embodiment of an electronic device.

Firstly, the control unit 105 calculates the speed of the host car byusing the vehicle-speed information supplied from the vehicle-speedsensor 103 and also calculates the position of the host car by using theposition information supplied from the GPS unit 104. Then, the controlunit 105 calculates the position and the speed of the preceding car byusing the information on the image of the preceding car taken by theimage pickup device 201 and information on the distance and the relativespeed between the preceding car and the host car detected by the sensor202, both of which are supplied from the detection unit 102, as well asthe information on the position and the speed of the host car. Thecontrol unit 105 monitors the position and the speed of the host car,and the position and the speed of the preceding car (step S101).

Next, the signal reception unit 101 receives traffic signal informationtransmitted by a road-side unit, such as an optical beacon, installed ina road-side position located, for example, 300 m before an intersectionwith a traffic light in the approaching direction, and the control unit105 determines whether or not it was able to acquire the receivedtraffic signal information from the signal reception unit 101 (stepS102). When the control unit 105 was not able to acquire the trafficsignal information from the signal reception unit 101, the control unit105 continues the monitoring in the step S101, whereas when the controlunit 105 was able to acquire the traffic signal information, the controlunit 105 proceeds to a step S103.

In the step S103, the control unit 105 predicts, based on the acquiredtraffic signal information, when the preceding car maintains the currentspeed, whether or not the preceding car goes into the intersectionlocated ahead of the host car and the preceding car in the travelingdirection thereof when the traffic light located in the intersection isin a red signal display state.

As described previously, the traffic signal information is informationincluding a current display state (red/yellow/blue) of the traffic lightlocated ahead of the host car in the traveling direction thereof and thenumber of seconds before the display of the traffic light changes fromblue to red or from red to blue next time. Therefore, when the currentdisplay state of the traffic light is in a blue signal display state,the control unit 105 can predict that the traffic light will change to ared signal display state, for example, in 12 seconds. In this state,assuming that the control unit 105 has obtained a monitoring resultindicating that the preceding car is traveling on the road 200 m beforethe intersection at 60 km per hour (i.e., 16.6 m per second) in the stepS101, the control unit 105 obtains a prediction result indicating thatwhen the preceding car maintains the current speed, the preceding carwill go into the intersection in 12 seconds, i.e., at the moment whenthe display state of the traffic light in the intersection changes tothe red signal display state in the step S103.

When the control unit 105 cannot obtain a prediction result indicatingthat the preceding car will go into the intersection where the trafficlight is in the red signal display state in the step S103, the controlunit 105 continues the monitoring process in the step S101, whereas whenthe control unit 105 can obtain a prediction result indicating that thepreceding car will go into the intersection where the traffic light isin the red signal display state, the control unit 105 proceeds to a stepS104 upon obtaining that decision result and gives the driver (the user)of the host car a first-stage warning. In the first-stage warning in thestep S104, information indicating that there is a possibility that thepreceding car will go into the intersection where the traffic light isin the red signal display state is displayed in the display unit 109 anda warning sound is produced by the sound output device 203. Note thatonly one of the warning display by the display unit 109 and the warningsound produced by the sound output device 203 may be used. Thisfirst-stage warning is not only for drawing the driver's attention tothe behavior of the preceding car because the host car following thepreceding car will also go into the intersection where the traffic lightis in the red signal display state as a matter of course, but also fordrawing the driver's attention to the speed of the host car.

Subsequent to the warning in the step S104, the control unit 105continues monitoring the position of the preceding car, the speed of thepreceding car, the distance between the preceding car and theintersection, and the number of seconds before the traffic light in theintersection changes to a red signal display (step S105). Next, thecontrol unit 105 determines whether or not it is the timing when thetraffic light ahead of the preceding and host cars in the travelingdirection thereof changes from a blue signal display state to a yellowsignal display state based on the previously received traffic signalinformation (step S106).

Note that the control unit 105 may use a state where the traffic lightahead of the preceding and host cars in the traveling direction thereofis in a yellow signal display state as the criterion for thedetermination in the step S106 based on newly received traffic signalinformation. Since the traffic signal information is provided through anoptical beacon, the control unit 105 is not necessarily able to receivenew traffic signal information at all times. Therefore, in the stepS106, either the previously received traffic signal information or thenewly received traffic signal information may be used. Alternatively, apriority may be given to a predetermined one of these traffic signalinformation items, or a priority may be given to the earlier one of theswitching timing that is calculated by using the previously receivedtraffic signal information and the switching timing that is calculatedby using the newly received traffic signal information.

Next, when the control unit 105 determines that it is the timing whenthe traffic light in the intersection changes from a blue signal displaystate to a yellow signal display state in the step S106, the controlunit 105 determines, at the timing when the traffic light changes to theyellow signal display state, whether or not the preceding car can stopsafely without braking suddenly based on the current speed of thepreceding car and the distance between the preceding car and theintersection (step S107). The determination in the step S107 is madewithin a period in which the traffic light blinks the yellow signaldisplay before changing from the yellow signal display state to a redsignal display state (e.g., within three to four seconds).

The determination process in the step S107 will now be explained in amore detailed manner. It is considered that it takes about one secondfrom when the driver decides to stop the vehicle to when the driverstarts braking. The distance that the vehicle travels in that one secondis called an “idle running distance”. A stopping distance is the sum ofthe idle running distance and a braking distance that is a distance thevehicle travels from when the driver actually applies the brakes to whenthe vehicle stops. Table 1 shows an example showing, in a state wherethe vehicle brakes suddenly, idle running distances, braking distances,and stopping distances versus speeds (km/h) of the vehicle under acondition that the road surface is dried.

TABLE 1 BRAKING STOPPING SPEED IDLE RUNNING DISTANCE DISTANCE [km/h]DISTANCE [m] [m] [m] 20 6 2 8 30 11 9 20 60 17 20 37 80 22 36 58 100 2856 84 120 33 81 114

Next, stopping distances in a case where the preceding car brakessuddenly and stops during the period of about three to four second inwhich the traffic light remains in a yellow signal display state (i.e.,stopping distances from the position of the preceding car at the momentwhen the traffic light changes to a yellow signal display state) areshown in the below Table 2.

TABLE 2 STOPPING DISTANCE OF PRECEDING CAR FROM POINT WHEN YELLOW SIGNALDISPLAY HAS CONTINUED 0 SECOND TIMING OF DETERMINATION ON STOP YELLOWYELLOW YELLOW YELLOW SIGNAL SIGNAL SIGNAL SIGNAL SPEED DISPLAY DISPLAYDISPLAY DISPLAY [km/h] 0 SECOND 1 SECOND 2 SECONDS 3 SECONDS 20 8 14 2026 30 20 31 42 53 60 37 54 71 88 80 58 80 102 124 100 84 112 140 168 120114 147 180 213

As seen from Table 2, for example, when the preceding car traveling at20 km/h brakes suddenly during the period of about three to four secondsin which the traffic light remains in the yellow signal display state,the preceding car stops after moving 8 m to 26 m from the place wherethe preceding car is located at the moment when the traffic lightchanged to the yellow signal display state. This means that when thedistance between the preceding car traveling at 20 km/h and theintersection is equal to or shorter than 8 m to 26 m, the preceding carcannot stop before the stop line located before the intersection unlessthe preceding car brakes suddenly.

Therefore, in the step S107, the control unit 105 determines, based onthe speed of the preceding car and the distance between the precedingcar and the intersection obtained at the moment when the traffic lightchanges to the yellow signal display state, whether or not the precedingcar can stop at the stop line located before the intersection withoutbraking suddenly by determining whether or not the distance between thepreceding car and the intersection corresponding to the speed of thepreceding car is equal to or shorter than the pre-defined thresholdshown in the below Table 3.

TABLE 3 DISTANCE BETWEEN PRECEDING CAR AND INTERSECTION AT POINT WHENTRAFFIC LIGHT CHANGES TO YELLOW SIGNAL DISPLAY SPEED THRESHOLD THRESHOLD[km/h] THRESHOLD SETTING 1 SETTING 2 SETTING 3 20 26 32 38 30 53 64 7560 88 105 122 80 124 146 168 100 168 196 224 120 213 246 279

Table 3 shows an example of settings in which the allowance (or margin)for determination using “Threshold Setting 2” is larger than that forthe determination using “Threshold Setting 1” and smaller than that ofthe determination using “Threshold Setting 3”. That is, when the“Threshold Setting 3” is adopted, the distance by which the precedingcar can stop by braking suddenly is estimated to be a larger value thanthose when the “Threshold Setting 1” or the “Threshold Setting 2” isadopted. Therefore, safety is the highest when the “Threshold Setting 3”is adopted. The driver can arbitrarily select any one of those threetypes of settings based on, for example, his/her driving skill and/orthe braking performance of the vehicle. Further, since the brakingdistance and the stopping distance become longer when it rains than whenthe road is dry, threshold settings for rainy weather may be separatelydefined. Further, the detection unit 102 may determine whether it israining or not based on image information output from the image pickupdevice 201 by using an image recognition technique, and thresholdsettings for rainy weather may be automatically adopted in rainyweather. Alternatively, the On/Off signal of windshield wipers may bedetected for determining whether it is raining or not.

FIG. 3 is a graph showing a relation shown in Table 3, i.e., a relationbetween speeds of the preceding car and distances to the intersectionobtained at the moment when the traffic light becomes a yellow signaldisplay state shown in Table 3 and three types of threshold settings. InFIG. 3, the line I indicates a characteristic (i.e., a relation) betweenspeeds of the preceding car and distances to the intersection when theThreshold Setting 1 is adopted. Further, the lines II and III indicatethese characteristics when Threshold Settings 2 and 3, respectively, areadopted.

In the step S107, when the control unit 105 determines that the distancebetween the preceding car and the intersection corresponding to thespeed of the preceding car at the moment when the traffic light changesto the yellow signal display state is equal to or shorter than thepre-defined threshold, the control unit 105 determines that thepreceding car cannot stop safely at the stop line position locatedbefore the intersection without braking suddenly (No at S107) and givesa second-stage warning (step S108). In the second-stage warning in thestep S108, information indicating that there is a risk that the host carcould bump into the preceding car because of the sudden braking by thepreceding car is displayed in the display unit 109 and a warning soundis produced by the sound output device 203. By doing so, the driver'sattention is drawn to the risk. Note that only one of the warningdisplay by the display unit 109 and the warning sound produced by thesound output device 203 may be used.

Further, it is preferable for the second-stage warning in the step S108to have a more urgent aspect and indicate a stronger risk than those ofthe first-stage warning in the step S104 in view of the emergency andthe risk. Further, the way of informing the driver of the warning in thefirst-stage warning may be changed in the second-stage warning. Forexample, while the first-stage warning may be to warn the driver bysuperposing the warning on the map image in the display unit 109, thesecond-stage warning may be to warn the driver by displaying only thewarning image over the entire screen of the display unit 109.Alternatively, the percentage of the area of the entire screen of thedisplay unit 109 occupied by the warning image may be changed. Forexample, the percentage of the area occupied by the warning image may be30% for the first-stage warning and 80% for the second-stage warning.That is, the warning may be differentiated by changing the size of thewarning image. Note that in the step S108, the driver of the host carcan be urged to reduce the speed by giving the driver the second-stagewarning. Therefore, even when the preceding car does not brake suddenlyand passes through the intersection where the traffic light is in thered-display state, it is possible, by urging the driver of the followinghost car to reduce the speed, to enable the driver of the host car tohave enough time to stop the host car at the stop line position locatedbefore the intersection where the traffic light is in the red-displaystate. This is also desirable in view of the safe driving.

The explanation is continued by referring to FIG. 2 again. In the stepS107, when the control unit 105 determines that the distance between thepreceding car and the intersection corresponding to the speed of thepreceding car at the moment when the traffic light changes to the yellowsignal display state is larger than the pre-defined threshold, i.e.,determines that the preceding car can stop at the stop line positionlocated before the intersection without braking suddenly (Yes at S107)or when the second-stage warning is given in the step S108, the controlunit 105 determines whether or not the above-described process should becontinued (step S109). Specifically, when the driver has made a requestfor terminating the process by entering an instruction or the likethrough the operation unit 108 or when there is no need to continue theprocess because the host car is parked or the like, the process is notcontinued. When the process should be continued, it returns to the stepS101.

As described above, according to the navigation device 100, which is anelectronic device according to this exemplary embodiment, it ispossible, by monitoring the positions and the speeds of the precedingcar and the host car and calculating the current speed of the precedingcar, distances from the preceding car to an intersection with a trafficlight located ahead of the host car and the preceding car in thetraveling direction thereof, and the timing when the traffic lightchanges its display state based on received traffic signal information,to predict whether or not the preceding car can stop at the stop lineposition located before the intersection without braking suddenly whenthe traffic light changes to the red signal display state at the pointof time when the host car receives the traffic light information and atthe point of time when the traffic light changes to the yellow signaldisplay state. Therefore, when it is predicted that the preceding carcannot stop at the stop line position located before the intersectionwithout braking suddenly, it is possible to warn in advance the driverof a risk that the host car could bump into the preceding car because ofthe sudden braking by the preceding car and thereby reduce thepossibility of a collision with the preceding car. Therefore, accordingto this embodiment, it is possible to inform the occupant of a risk thatthe host car could bump into the preceding car by predicting the stop ofthe preceding car.

Next, an operation in a second exemplary embodiment is explained. FIG. 4is a flowchart for explaining an operation in the second exemplaryembodiment of an electronic device. In FIG. 4, the same symbols as thosein FIG. 2 are assigned to the same process steps as those shown in FIG.2 and their explanations are omitted. In this exemplary embodiment,processes in steps S111 to S113 are performed in place of the processesin the step S107 and the subsequent steps in the flowchart shown in FIG.2. In this exemplary embodiment, after the preceding car increases itsspeed when or after the traffic light changes to a yellow signal displaystate, there is a possibility that the preceding car could brakesuddenly immediately before the preceding car goes into the intersectiondue to a red signal display of the traffic light or the like. Therefore,a warning is given to the driver.

That is, when the control unit 105 determines that it is the timing whenthe traffic light in the intersection changes from a blue signal displaystate to a yellow signal display state in the step S106 in FIG. 4, thecontrol unit 105 determines, at the timing when the traffic lightchanges to the yellow signal display state, whether or not the precedingcar has increased its speed by using, for example, image-takinginformation of the image pickup device 201 (step S111). When the controlunit 105 determines that the preceding car has increased the speed inthe step S111, the control unit 105 predicts that there is a possibilitythat the preceding car cannot stop safely, for the red signal displaystate of the traffic light or the like, at the stop line positionlocated before the intersection without braking suddenly because thepreceding car has increased the speed and hence gives a third warning,which is a warning against the collision or the like, by using a sound,an image display, and/or the like (step S112).

On the other hand, when the control unit 105 determines that thepreceding car has not increased the speed in the step S111, the controlunit 105 determines whether or not the process should be continued (stepS113). When the third warning is given in the step S112, the controlunit 105 also determines whether or not the process should be continued(step S113). When the driver has made a request for terminating theprocess by entering an instruction or the like through the operationunit 108 or when there is no need to continue the process because thehost car is parked or the like, the process is not continued. When theprocess should be continued, it returns to the step S101. Note that theprocess in the second exemplary embodiment may be combined with theprocess in the first exemplary embodiment, or may be combined withprocesses in the below-shown other exemplary embodiments.

Next, an operation in a third exemplary embodiment is explained. FIG. 5is a flowchart for explaining an operation in the third exemplaryembodiment of an electronic device. In FIG. 5, the same symbols as thosein FIG. 2 are assigned to the same process steps as those shown in FIG.2 and their explanations are omitted. In this exemplary embodiment,processes in steps S121 to S123 are performed in place of the processesin the step S107 and the subsequent steps in the flowchart shown in FIG.2. In the third exemplary embodiment, when the preceding car turns on ablinker (i.e., a turn-signal) when or after the traffic light changes toa yellow signal display state, there is a possibility that the precedingcar could brake suddenly in order to turn right or left at theintersection. Therefore, a warning is given to the driver.

That is, when the control unit 105 determines that it is the timing whenthe traffic light in the intersection changes from a blue signal displaystate to a yellow signal display state in the step S106 in FIG. 5, thecontrol unit 105 determines, at the timing when the traffic lightchanges to the yellow signal display state, whether or not the precedingcar has turned on a blinker by using, for example, image-takinginformation of the image pickup device 201 (step S121). When the controlunit 105 determines that the preceding car has turned on the blinker inthe step S121, the control unit 105 predicts that there is a possibilitythat the preceding car could brake suddenly in order to turn right orleft in the intersection and hence gives a fourth warning, which is awarning against the collision or the like, by using a sound, an imagedisplay, and/or the like (step S122). On the other hand, when thecontrol unit 105 determines that the preceding car has not turned on theblinker in the step S121, the control unit 105 determines whether or notthe process should be continued (step S123). When the fourth warning isgiven in the step S122, the control unit 105 also determines whether ornot the process should be continued (step S123). When the driver hasmade a request for terminating the process by entering an instruction orthe like through the operation unit 108 or when there is no need tocontinue the process because the host car is parked or the like, theprocess is not continued. When the process should be continued, itreturns to the step S101. Note that the process in the third exemplaryembodiment may be combined with at least one of the processes in thefirst and second exemplary embodiments, or may be combined withprocesses in the below-shown other exemplary embodiments.

Next, an operation in a fourth exemplary embodiment is explained. FIG.6A is a flowchart for explaining an operation in the fourth exemplaryembodiment of an electronic device. In FIG. 6A, the same symbols asthose in FIG. 2 are assigned to the same process steps as those shown inFIG. 2 and their explanations are omitted. In this exemplary embodiment,processes in steps S131 to S133 are performed in place of the processesin the step S107 and the subsequent steps in the flowchart shown in FIG.2. In the fourth exemplary embodiment, it is determined, when or afterthe traffic light changes to a yellow signal display state, whether ornot, when the navigation device is guiding the host car to move to anext lane, a preceding car that is present in the next lane couldpossibly brake suddenly. Then, a warning is given to the driver.

In this case, when the control unit 105 determines that it is the timingwhen the traffic light in the intersection changes from a blue signaldisplay state to a yellow signal display state in the step S106 in FIG.6A, then the control unit 105 determines, at the timing when the trafficlight changes to the yellow signal display state, whether or not thenavigation device is guiding the host car to a next lane and a precedingcar that is present in the next lane could possibly brake suddenly (stepS131 in FIG. 6A). That is, in the step S131, as shown in FIG. 6B as anexample, when the navigation device is guiding the host car 11 to moveto a next lane for a right-turn (hereinafter called a “right-turn lane”)in order to turn right at the next intersection, a vehicle that istraveling in a sensing area (i.e., a detection area) SA located ahead ofthe host car 11 in the traveling direction thereof and traveling in thenext right-turn lane will become a preceding car 21 after the lanechange. Therefore, the control unit 105 predicts whether or not thepreceding car 21 will go into the next intersection at a timing when thetraffic light in the next intersection is in a red signal display state,i.e., whether or not there is a possibility that the host car 11 couldbump into the preceding car 21 because the preceding car 21 could brakesuddenly at the intersection based on the current speed of the precedingcar 21 and the distance between the preceding car 21 and the nextintersection.

When the control unit 105 determines that there is a possibility thatthe preceding car traveling in the next lane could brake suddenly in thestep S131, the control unit 105 warns, as a fifth warning, the driver ofthe possibility of the collision by using a sound, an image display,and/or the like (step S132 in FIG. 6A). On the other hand, when thecontrol unit 105 determines that the navigation device is not guidingthe host car to the next lane, that there is no behavior indicating themove to the next lane, that no preceding car is present in thedestination lane, i.e., in the next lane, or that the preceding car isnot expected to brake suddenly because the preceding car is already in astopped state or the like in the step S131 (No at step S131), thecontrol unit 105 determines whether or not the process should becontinued (step S133). When the fifth warning is given in the step S132,the control unit 105 also determines whether or not the process shouldbe continued (step S133). When the driver has made a request forterminating the process by entering an instruction or the like throughthe operation unit 108 or when there is no need to continue the processbecause the host car is parked or the like, the process is notcontinued. When the process should be continued, it returns to the stepS101. Note that the process in the fourth exemplary embodiment may becombined with at least one of the processes in the first to thirdexemplary embodiments, or may be combined with the below-shownprocesses. Further, the determination on whether or not the precedingcar in the next lane will brake suddenly may be made by using the samecriterion as that used in the determination on the sudden brakingperformed by the preceding car traveling in the same lane as that of thehost car as in the case of the first exemplary embodiment.Alternatively, the prediction/determination on the sudden braking may bemade by using other methods.

Next, an operation in a fifth exemplary embodiment is explained. FIG. 7Ais a flowchart for explaining an operation in the fifth exemplaryembodiment of an electronic device. In FIG. 7A, the same symbols asthose in FIG. 2 are assigned to the same process steps as those shown inFIG. 2 and their explanations are omitted. In this exemplary embodiment,processes in steps S141 to S143 are performed in place of the processesin the step S107 and the subsequent steps in the flowchart shown in FIG.2. In this exemplary embodiment, it is predicted, when the navigationdevice is guiding the host car to move to a next lane, whether or not apreceding car present in the next lane is in a situation in which afterthe preceding car has increased its speed while a traffic light is in ayellow signal display state, the preceding car almost goes into anintersection while the traffic light is in a red signal display stateand, as a result, the preceding car brakes suddenly. Then, a warning isgiven to the driver.

In this case, when the control unit 105 determines that it is the timingwhen the traffic light in the intersection changes from a blue signaldisplay state to a yellow signal display state in the step S106 in FIG.7A, then the control unit 105 determines, at the timing when the trafficlight changes to the yellow signal display state, whether or not thenavigation device is guiding the host car to a next lane and a precedingcar that is present in the next lane has increased its speed (step S141in FIG. 7A). That is, in the step S141, as shown in FIG. 7B as anexample, when the navigation device is guiding the host car 11 to moveto a next right-turn lane in order to turn right at the nextintersection, a vehicle that is traveling in a sensing area (i.e., adetection area) SA located ahead of the host car 11 in the travelingdirection thereof and traveling in the next right-turn lane will becomea preceding car 22 after the lane change. Therefore, the control unit105 determines whether or not the preceding car 22 has increased itsspeed, and when the control unit 105 determines that the preceding carhas increased the speed, predicts that there is a possibility that thepreceding car cannot stop safely, for the red signal display state ofthe traffic light or the like, at the stop line position located beforethe intersection without braking suddenly because the preceding car hasincreased the speed.

When the control unit 105 determines that the preceding car hasincreased the speed in the step S141, the control unit 105 gives, as asixth warning, a warning indicating that the preceding car has increasedthe speed and/or a warning against the collision or the like because ofthe possibility that the preceding car is about to go into theintersection at the timing when the traffic light is in the red signaldisplay state and hence the preceding car could brake suddenly at theintersection by using a sound, an image display, and/or the like (stepS142 in FIG. 7A). On the other hand, when the control unit 105determines that the navigation device is not guiding the host car to thenext lane, that there is no behavior indicating the move to the nextlane, that no preceding car is present in the destination lane, i.e., inthe next lane, or that the preceding car in the next lane has notincreased the speed in the step S141 (No at step S141), the control unit105 predicts that the preceding car will not brake suddenly anddetermines whether or not the process should be continued (step S143).When the sixth warning is given in the step S142, the control unit 105also determines whether or not the process should be continued (stepS143). When the driver has made a request for terminating the process byentering an instruction or the like through the operation unit 108 orwhen there is no need to continue the process because the host car isparked or the like, the process is not continued. When the processshould be continued, it returns to the step S101.

Note that the process in the fifth exemplary embodiment may be combinedwith at least one of the processes in the first to fourth exemplaryembodiments, or may be combined with the below-shown processes. Further,the determination on whether or not the preceding car in the next lanehas increased its speed may be made by using the same criterion as thatused in the determination on the increase in the speed of the precedingcar traveling in the same lane as that of the host car as in the case ofthe second exemplary embodiment. Alternatively, the determination on theincrease in the speed may be made by using other methods.

Next, an operation in a sixth exemplary embodiment is explained. FIG. 8Ais a flowchart for explaining an operation in the sixth exemplaryembodiment of an electronic device. In FIG. 8A, the same symbols asthose in FIG. 2 are assigned to the same process steps as those shown inFIG. 2 and their explanations are omitted. In this exemplary embodiment,processes in steps S151 to S153 are performed in place of the processesin the step S107 and the subsequent steps in the flowchart shown in FIG.2. In this exemplary embodiment, it is predicted, when the navigationdevice is guiding the host car to move to a next lane, whether or not apreceding car present in the next lane is in a state in which thepreceding car turns on a blinker and could brake suddenly in order toturn right or left. Then, a warning is given to the driver.

In this case, when the control unit 105 determines that it is the timingwhen the traffic light in the intersection changes from a blue signaldisplay state to a yellow signal display state in the step S106 in FIG.8A, then the control unit 105 determines, at the timing when the trafficlight changes to the yellow signal display state, whether or not thenavigation device is guiding the host car to a next lane and a precedingcar that is present in the next lane turns on a blinker (step S151 inFIG. 8A). That is, in the step S151, as shown in FIG. 8B as an example,when the navigation device is guiding the host car 11 to move to a nextright-turn lane in order to turn right at the next intersection, avehicle that is traveling in a sensing area (i.e., a detection area) SAlocated ahead of the host car 11 in the traveling direction thereof andin the next right-turn lane will become a preceding car 23 after thelane change. Therefore, the control unit 105 determines whether or notthe preceding car 23 has turned on a blinker to turn right, and when thecontrol unit 105 determines that the preceding car 23 has turned on theblinker, predicts that there is a possibility that the preceding car 23could brake suddenly and, as a result, the host car 11 could bump intothe preceding car 23.

When the control unit 105 determines that the navigation device isguiding the host car to move to a next lane and a preceding car presentin the next lane has turned on a blinker in the step S151, the controlunit 105 determines that there is a possibility that the host car couldbump into the preceding car and gives a seventh warning by using asound, an image display, and/or the like (step S152 in FIG. 8A). On theother hand, when the control unit 105 determines that the navigationdevice is not guiding the host car to the next lane, that there is nobehavior indicating the move to the next lane, that no preceding car ispresent in the destination lane, i.e., in the next lane, or that thepreceding car in the next lane has not turned on a blinker in the stepS151 (No at step S151), the control unit 105 predicts that the precedingcar will not brake suddenly and determines whether or not the processshould be continued (step S153). When the seventh warning is given inthe step S152, the control unit 105 also determines whether or not theprocess should be continued (step S153). When the driver has made arequest for terminating the process by entering an instruction or thelike through the operation unit 108 or when there is no need to continuethe process because the host car is parked or the like, the process isnot continued. When the process should be continued, it returns to thestep S101.

Note that the process in the sixth exemplary embodiment may be combinedwith at least one of the processes in the first to fifth exemplaryembodiments. Further, the determination on whether or not the precedingcar in the next lane has turned on a blinker may be made by using thesame criterion as that used in the determination on the turning-on ofthe blinker of the preceding car traveling in the same lane as that ofthe host car as in the case of the third exemplary embodiment.Alternatively, the determination on the turning-on of a blinker may bemade by using other methods.

Note that the present invention is not limited to the above-describedexemplary embodiments and includes the below-shown various modifiedexamples. For example, although it is explained that the second-stagewarning informs the driver that there is a possibility of a collisionand thereby urges the driver to perform a speed-reducing operation inthe above-described exemplary embodiments, the vehicle may be forciblycontrolled so that its speed is reduced without having the driverperform the speed-reducing operation.

Further, when there is a possibility that a preceding car goes into anintersection where a traffic light is in a red signal display state, itmay be determined that the behavior of the preceding car could be in onethe following two states: (1) the preceding car goes into theintersection and passes through the intersection without brakingsuddenly; and (2) the preceding car brakes suddenly and hence there is apossibility of a collision. This determination can be made bydetermining whether a brake light of the preceding car is turned on ordetecting the change in the speed of the preceding car.

That is, if the speed of the preceding car does not change or thepreceding car is accelerating when or after the traffic light changes toa yellow signal display state, it may be determined that there is apossibility that the preceding car will pass through the intersectionwhere the traffic light is in a red signal display state and hence nowarning may be given. Alternatively, when the preceding car isaccelerating, it may be determined that the possibility that thepreceding car brakes suddenly is higher and hence the third-stagewarning may be given. When it is detected that a brake light is turnedon, it may be determined that the possibility that the preceding carwill stop is high. Further, the possibility of a collision may bedetermined based on the speeds of the preceding car and the host car atthat moment, and it may be determined whether or not a warning should beoutput.

Further, in the step S106, the determination of the state in which thetraffic light becomes a yellow signal display state may be made bytaking an image of the traffic light located ahead of the host car byusing the image pickup device 201 and recognizing that the traffic lightis yellow by the detection unit 102.

Further, as the condition for issuing a warning in the steps S104 andS108, at least one of the following conditions may be added: (1) thespeed of the host car is equal to or higher than a certain speed; (2)the relative speed between the host car and the preceding car is equalto or higher than a certain speed; and (3) the distance between the hostcar and the preceding car is equal to or shorter than a certaindistance.

Further, although the position of the preceding car and the relativespeed between the host car and the preceding car are calculated by thedetection unit 102 based on image information of the preceding car takenby the image pickup device 201 and information detected by the sensor202 in the step S101, the position of the preceding car and the relativespeed between the host car and the preceding car may be calculated bythe detection unit 102 based on only one of the image information of thepreceding car taken by the image pickup device 201 and informationdetected by the sensor 202.

Note that the present invention includes a control method for anelectronic device performing the processes explained above withreference to the flowcharts shown in FIGS. 2, 4, 5, 6A, 7A and 8A, and acontrol program for an electronic device executed by a software processof a computer. The control program for an electronic device may bedistributed through a communication network and downloaded into acomputer, or may be recoded in a recording medium, distributed throughthe recording medium, and installed into a computer.

Although the present invention has been explained with reference tocertain exemplary embodiments, the present invention is not limited tothose exemplary embodiments. Various modifications can be made to theconfigurations and the details of those exemplary embodiments by thoseskilled in the art without departing from the spirit and scope of thepresent invention.

What is claimed is:
 1. An electronic device comprising: a monitor unitconfigured to monitor a traveling speed and a traveling position of ahost car, and a speed and a position of a preceding car, the host carbeing a vehicle in which the electronic device is mounted, the precedingcar being a vehicle traveling ahead of the host car; a reception unitconfigured to receive traffic signal information including at least acurrent display state of a traffic light in an intersection locatedahead of the host car in a traveling direction and timing information ofa change of the display state of the traffic light; a prediction unitconfigured to generate a first prediction result of a prediction whetheror not the preceding car will go into the intersection after the trafficlight changes to a red signal display state when the preceding carmaintains a current speed based on monitor information and the trafficsignal information received by the reception unit, and generate, at atiming when the traffic light becomes the yellow signal display state, asecond prediction result of a prediction whether or not the precedingcar can stop before the intersection without braking suddenly based onthe position and the speed of the preceding car and a distance betweenthe preceding car and the intersection, the monitor informationincluding the traveling speed and the traveling position of the host carand the speed and the position of the preceding car monitored by themonitor unit; and a warning unit configured to give a first-stagewarning when the first prediction result indicates that the precedingcar will go into the intersection after the traffic light changes to thered signal display state, and give a second-stage warning when thesecond prediction result indicates that the preceding car cannot stopbefore the intersection without braking suddenly.
 2. The electronicdevice according to claim 1, wherein the prediction unit generates thesecond prediction result within a period in which the current displaystate of the traffic light is determined to be a yellow signal displaystate based on the received traffic signal information.
 3. Theelectronic device according to claim 1, wherein the prediction unitgenerates a third prediction result when at least one of an increase inthe speed of the preceding car and turning-on of a blinker of thepreceding car is detected after the current display state of the trafficlight is determined to be the yellow signal display state based on thereceived traffic signal information, and the warning unit warns the userof host car based on the third prediction result.
 4. A control methodfor an electronic device comprising: a monitoring step for monitoring atraveling speed and a traveling position of a host car, and a speed anda position of a preceding car, the preceding car being a vehicletraveling ahead of the host car; a receiving step for receiving trafficsignal information including at least a current display state of atraffic light in an intersection located ahead of the host car in atraveling direction and timing information of a change of the displaystate of the traffic light; a predicting step for generating a firstprediction result of a prediction whether or not the preceding car willgo into the intersection after the traffic light changes to a red signaldisplay state when the preceding car maintains a current speed based onmonitor information and the traffic signal information received in thereceiving step, and generating, at a timing when the traffic lightbecomes the yellow signal display state, a second prediction result of aprediction whether or not the preceding car can stop before theintersection without braking suddenly based on the position and thespeed of the preceding car and a distance between the preceding car andthe intersection, the monitor information including the traveling speedand the traveling position of the host car and the speed and theposition of the preceding car monitored in the monitoring step; and awarning step for giving a first-stage warning when the first predictionresult indicates that the preceding car will go into the intersectionafter the traffic light changes to the red signal display state, andgiving a second-stage warning when the second prediction resultindicates that the preceding car cannot stop before the intersectionwithout braking suddenly.
 5. A control program for an electronic devicefor causing a computer to execute: a monitoring step for monitoring atraveling speed and a traveling position of a host car, and a speed anda position of a preceding car, the preceding car being a vehicletraveling ahead of the host car; a receiving step for receiving trafficsignal information including at least a current display state of atraffic light in an intersection located ahead of the host car in atraveling direction and timing information of a change of the displaystate of the traffic light; a predicting step for generating a firstprediction result of a prediction whether or not the preceding car willgo into the intersection after the traffic light changes to a red signaldisplay state when the preceding car maintains a current speed based onmonitor information and the traffic signal information received in thereceiving step, and generating, at a timing when the traffic lightbecomes the yellow signal display state, a second prediction result of aprediction whether or not the preceding car can stop before theintersection without braking suddenly based on the position and thespeed of the preceding car and a distance between the preceding car andthe intersection, the monitor information including the traveling speedand the traveling position of the host car and the speed and theposition of the preceding car monitored in the monitoring step; and awarning step for giving a first-stage warning when the first predictionresult indicates that the preceding car will go into the intersectionafter the traffic light changes to the red signal display state, andgiving a second-stage warning when the second prediction resultindicates that the preceding car cannot stop before the intersectionwithout braking suddenly.